Macrophage(MO)-colony stimulating factor (M-CSF) importantly contributes to the development of atherosclerotic lesions. We have found that the absence of M-CSF in atherosclerosis-prone apolipoprotein (apo) E or low-density lipoprotein receptor (LDLR)- deficient mice results in substantially reduced atherosclerosis despite augmented hypercholesterolemia. Our most recent studies provide compelling evidence in favor of a direct local effect of M-CSF within the vessel wall. These advances, together with the characterization of the M-CSF-mediated induction of urokinase plasminogen activator (uPA) and matrix metalloproteinases (MMPs) cascade have prompted more refined questions on the molecular mechanisms responsible for the full range of M-CSF actions in the diseased vessel wall. In this proposal, we seek to extend our research efforts to understand the role of M-CSF in the development and disruption of arterial lesions by testing following three hypotheses: 1) pleiotropic effects of M-CSF on intimal MO and SMC are modulated mainly through the activation of nuclear factors downstream to the Ras-mediated cell signaling pathways. One such factor is the transcription factor Ets-2 that promotes cell proliferation and survival, 2) increased M-CSF activity in atherosclerotic lesions contributes to the MO -mediated matrix remodeling by up regulating the expression of uPA and MT3-MMP genes. This effect of M-CSF may play a role in plaque disruption, and 3) M-CSF up regulates the MO-specific transcription of uPA and MT3-MMP genes by activating a common set of trans-acting factors (such as Ets family of transcription factors) that form ternary complexes with AP-l and bind to cis-acting DNA elements present in the 5' regulatory region of these genes. The specific aims are: 1) to investigate the effects of M-CSF on the growth of arterial lesion-associated cells in vivo using mice lacking M-CSF and/or apoE and to perform in vitro studies using cultured cells from M-CSF-deficient mice to determine the mechanism(s) underlying the M-CSF mediated proliferation and survival of MO and SMC, 2) to determine the effects of M-CSF on the expression of uPA and MT3-MMP in cultured MO and to examine the association of M-CSF regulated production of uPA and MT3-MMP to alterations in the character of atherosclerotic lesions, and 3) to identify the cis-acting elements in the uPA and MT3-MMP promoters that mediate the inductive effects of M-CSF on the expression of these genes and to examine the signaling events connecting M-CSF with the nuclear regulators of uPA and MT3-MMP. We believe our studies will provide new and important information regarding the role of M-CSF in the development and disruption of atherosclerotic and proliferative vascular lesions and this information may prove useful in design of novel therapeutic interventions for vascular diseases.